220.7 PROJECT SUMMARY/ABSTRACT Stigma is a pervasive barrier to HIV testing and PrEP use among US Latino men who have sex with men (LMSM). Routine HIV testing and large scale PrEP coverage are essential HIV prevention strategies for ending the HIV epidemic. LMSM further contend with intersectional stigma, meaning they experience or fear unjust treatment from others due to their ethnic, sexual, and masculine identities (i.e. adherence to masculinity norms). Specific to intersectional stigma, emerging quantitative research suggests exposure to stigma towards >1 intersectional identity is associated with worse health outcomes than exposure to stigma towards a single intersectional identity. While research on intersectional stigma has been largely qualitative, advanced quantitative methods offer an opportunity to identify novel actionable intervention mechanisms and targets; improving our public health response to ending the US HIV epidemic. Social network analysis is a robust method for examining how LMSM interact with and are affected by others in their social network. Social networks are important intervention targets, since network members are capable of (1) stigmatizing LMSM (i.e. stigma sources) and (2) fostering resilience and social support to reduce the negative impact of intersectional stigma on LMSM?s HIV testing and PrEP use. The current study will prospectively assess how anticipated and enacted intersectional stigma are experienced by LMSM in their social networks at baseline to effect HIV testing and PrEP use 12-months post-baseline. We will recruit 500 HIV-negative adult LMSM from MSM and Latino community organizations. Study measures, including an egocentric social network inventory, will be collected at Months 0, 6, and 12. Our primary outcomes, HIV testing and PrEP use, will be abstracted from medical records at Month 12. We will use social network analysis to: (1) Identify how LMSM experience intersectional stigma in their social networks across diverse social context (i.e. types of social relationships [e.g. family, friends, sex partners, providers], expression of intersectional identities [e.g. acculturation, outness, masculinity]) (AIM 1, primary). (2) Prospectively evaluate the effect of social network exposure to intersectional stigma on HIV testing and PrEP use (AIM 2, primary). (3) Identify novel points of intervention to reduce the harmful effects of intersectional stigma on HIV testing and PrEP use (AIMS 3-4, exploratory) and develop data?and?community-informed intervention strategies for future piloting. As the first study to use social networks to evaluate the effects of intersectional stigma on health outcomes, NEXUS is significant because new HIV diagnoses among US LMSM are increasing?due to low rates of HIV testing (undiagnosed HIV) and PrEP use?while new diagnoses among non-LMSM have stabilized or decreased. A SN approach to studying intersectional stigma is highly innovative because it reflects a substantial departure from how intersectional stigma has been studied, opening new opportunities to end the HIV epidemic. Without such efforts, intersectional stigma will persist in producing and maintaining HIV disparities among LMSM.